Overview
This lecture covers the core principles of cell biology, including cell structure, cell specialisation, microscopy, culturing microorganisms, cell division, stem cells, and transport in cells, as outlined in AQA GCSE Biology Topic 1.
Cell Structure: Eukaryotes and Prokaryotes
- Eukaryotic cells (animal and plant) contain a nucleus, cytoplasm, and cell membrane.
- Prokaryotic cells (bacteria) are smaller, lack a nucleus, and have cell wall, membrane, cytoplasm, circular DNA, and plasmids.
- Organelles are specialised structures within cells.
- Orders of magnitude and metric prefixes (centi, milli, micro, nano) indicate the size differences between cells.
Subcellular Structures: Functions
- Nucleus: contains DNA, controls cell activities.
- Cytoplasm: site of chemical reactions, contains enzymes.
- Cell membrane: controls passage of substances.
- Mitochondria: site of aerobic respiration, energy release.
- Ribosomes: protein synthesis.
- In plants: chloroplasts (photosynthesis), permanent vacuole (support), cell wall (strength).
Cell Specialisation and Differentiation
- Differentiation gives cells specialised functions; animals mostly differentiate early, plants can throughout life.
- Animal specialised cells: sperm (movement, enzymes), nerve (long axons, dendrites), muscle (contraction proteins, mitochondria).
- Plant specialised cells: root hair (surface area for absorption), xylem (transport water, lignin), phloem (food transport, sieve plates).
- Stem cells can become specialised; adult stem cells replace some lost cells.
Microscopy and Calculations
- Light microscopes: lower magnification and resolution; view cells, tissues.
- Electron microscopes: high magnification, view organelles.
- Magnification = eyepiece × objective lens; Size = image size ÷ magnification.
Culturing Microorganisms
- Microorganisms are grown in nutrient broth or agar plates; strict sterilisation needed to avoid contamination.
- Bacteria multiply by binary fission; population = initial × 2^(number of divisions).
- Antibiotic effectiveness tested with inhibition zones on agar.
Cell Division: Mitosis and Chromosomes
- Chromosomes (DNA coils) carry genes; humans have 23 pairs.
- Cell cycle: interphase (growth, DNA replication), mitosis (chromosome separation), cytokinesis (cell splits).
- Mitosis produces genetically identical daughter cells; crucial for growth, repair, asexual reproduction.
Stem Cells and Therapeutic Cloning
- Embryonic stem cells can form any body cell; adult stem cells have limited potential; meristems in plants allow full differentiation.
- Therapeutic cloning produces stem cells genetically identical to patient.
- Benefits: disease treatment; Problems: ethical issues, risk of infection, technical challenges.
Transport in Cells: Diffusion, Osmosis, Active Transport
- Diffusion: passive movement from high to low concentration (e.g., gas exchange in lungs).
- Factors: concentration gradient, surface area to volume ratio, temperature.
- Adaptations: large surface area, thin membranes, efficient blood supply.
- Osmosis: water moves from dilute to concentrated solutions through partially permeable membrane; essential for cell turgor.
- Active transport: energy-dependent uptake against concentration gradient (e.g., minerals in roots, glucose in gut).
Key Terms & Definitions
- Eukaryote — cell with a nucleus and organelles.
- Prokaryote — cell without a nucleus.
- Organelle — specialised cell structure for a specific function.
- Mitosis — cell division producing identical cells.
- Stem cell — undifferentiated cell with the potential to specialise.
- Diffusion — passive movement of particles from high to low concentration.
- Osmosis — movement of water through a partially permeable membrane.
- Active transport — energy-requiring movement against concentration gradient.
- Magnification — ratio of image size to real size.
Action Items / Next Steps
- Review diagrams of cell structures and specialised cells.
- Practice microscopy calculations and binary fission problems.
- Complete assigned reading on stem cell ethics and applications.
- Prepare for practicals on osmosis and culturing bacteria.